A list of pertinent factors, to be of real use in the solution of problems, is required, first, to be complete, so that no factor will be overlooked, and, second, to be simple, so that, as far as practicable, all similar data may be discussed under one heading. With respect to the factors set forth in succeeding pages, the solution of a particular problem may call for a different listing. Such listing may involve, in some cases, the contraction or the omission of certain of the headings. In other cases, an expansion will be necessary or desirable under certain headings, in considerably greater detail than shown here. For example, Section I-B of a National Estimate may involve reference to several volumes of printed books or of similar data, while, even in ordinary strategical situations, numerous charts, books of sailing directions, and other compilations may require study. Where such references are not standard and generally available, they may be appended, preferably in condensed form. The proper listing of pertinent factors will depend on the nature of the problem. (1) Survey of the Means Available and Opposed. The application of power, actually or by threat, is dependent on the ability of the human and material components of fighting strength to develop energy and to exert effort for purposes of combat (page 8). These components, as ranged on one side or the other, constitute the means available and opposed. (See page 31). Analysis of these means requires a classification of the various factors which influence the situation. For a broad strategical estimate made by the State, economic and political factors require intensive study; physical objectives, relative position, apportionment of fighting strength, and freedom of action are all involved in such a survey. For a strategical estimate made by a high military commander, these factors frequently enter to a lesser extent. Such a commander is concerned only with the effect which these factors will have on the operations projected for the particular theater involved in his problem. From his point of view, the economic and political factors often have little bearing on the elements of a favorable military situation. In such a case, the commander concentrates in this section on the factors more directly relating to the armed forces; his important considerations deal with such matters as numerical strength, types of weapons, disposition, and factors as to freedom of action. For strategical estimates of lesser scope, the commander further restricts his study accordingly.